Condenser microphones span the range from telephone transmitters, karaoke microphones to high fidelity recording microphones. In a condenser microphone, also known as a capacitor or electrostatic microphone, a diaphragm or membrane acts as one plate of a capacitor, and the vibrations caused by sound waves produce changes in the distance between the membrane and the other plate; the back plate. A polarizing voltage is applied over the two plates, and the capacitance change provides the output from the device.
Throughout the prior art, the transducer membranes used are predominantly of circular shape. One example of a condenser microphone with a non circular membrane is shown in U.S. Pat. No. 3,814,864 wherein the diaphragm is broken up into many small pieces so that each attains a natural high frequency resonance above the range of sounds to be picked up with the sum total of the pieces providing an output as great as a single diaphragm with a lower impedance. This is achieved by providing a series of concentric ring contacts with a diaphragm stretched over the rings, the highest points or ridges of which lie on a convex surface, to break up the diaphragm into annular sections.
In WO2007/004981 a condenser microphone with a triangular transducer membrane and a corresponding back plate is disclosed. The back plate of this microphone consists of a solid machined copper plate, which is expensive to manufacture.